1. Field of the Invention
The invention relates to a road milling machine for the treatment of road pavements, as well as to a method for pivoting a travelling drive unit of a road milling machine.
2. Description of the Prior Art
A road milling machine is known, for example, from EP 916 004 A and U.S. Pat. No. 6,106,073.
Such road milling machine comprises a controller for the travelling, steering and milling operation, said controller being operated by an operator, and is provided with a machine frame adjustable in height via lifting columns.
Travelling drive units are arranged at the lower ends of the lifting columns which may be designed as wheeled travelling drive units or tracked travelling drive units. In this arrangement, it is also possible to have a mixture of wheeled and tracked travelling drive units.
A working drum revolving about an axis is arranged at the machine frame.
No less than one of the rear lifting columns with travelling drive unit attached thereto is pivotable by means of a pivoting arm from a first, outer end position projecting laterally relative to the machine frame to a second, inner end position wholly or in part within the machine frame. The inner position is required in order to be able to drive as closely along obstacles as possible with the so-called zero side of the road milling machine, where the zero side of a road milling machine is that side on which a front end of the working drum extends as closely as possible to the outer side of the road milling machine.
The pivotable travelling drive unit is also provided with a steering device which can adjust a steering angle for the travelling drive unit that deviates from straight-ahead travel. One driving device each is intended for driving the pivoting arm and for driving the steering device.
In such road milling machines, the travelling drive unit needs to be raised in order to move it from one end position to the other end position irrespective of whether the lifting column is guided by a single pivoting arm, or by two pivoting arms articulated in a parallelogram-like fashion, or in a different fashion. To this end, the machine frame needs to be raised in a first step, at least at the rear travelling drive units, until the working drum has a certain distance from the road surface. In order to protect the working drum, a wooden beam, for example, then needs to be pushed under the working drum so that the same does not rest on the ground and there is no possibility of damaging the milling tools when the pivotable travelling drive unit is raised in order to be able to pivot it without being in contact with the ground surface.